1. Field of the Invention
The present invention relates to a backlight unit, and more particularly, to a backlight unit capable of being used in the lighting of a display device or the like by employing a light emitting device as a light source.
2. Description of the Related Art
In general, a liquid crystal display (LCD), currently a common thin display device, has been applied to various devices, such as a wall-mounted type television, a notebook computer, a monitor for a desktop computer, a navigation system, a personal digital assistant (PDA), a cellular phone, and a portable computer game console or the like. A liquid crystal constituting the display device of the liquid crystal display may not emit light by itself, and may merely perform a simple function of transmitting or blocking light according to an electrical signal applied thereto.
Accordingly, in order to display information on a liquid crystal panel, a so-called surface light emitting device for irradiating the liquid crystal panel from the rear, a backlight unit needs to be separately provided in a liquid crystal display. Such a backlight unit may need to increase the luminance of light and form an even surface light source to irradiate light onto a liquid crystal panel, which is very important in view of product quality.
Since a general backlight unit has a small size and a long lifespan and directly converts electrical energy into optical energy, a light emitting diode (LED), having advantages such as high energy efficiency and a low operating voltage, has been used as a light source for the backlight unit.
In addition, backlight units are classified into an edge type backlight unit (side view type) and a direct type backlight unit (top view type) based on the mounting position of a light source. In the edge type backlight unit, a bar-shaped light source is located at the side of a liquid crystal panel to irradiate light towards the liquid crystal panel via a light guiding plate. In contrast with the edge type backlight unit, the direct type backlight unit directly irradiates light onto the liquid crystal panel from a surface light source disposed under the liquid crystal panel.
With the recent trend towards large, thin, highly functional image display devices, research into the realization of a backlight having a reduced thickness while exhibiting superior optical characteristics by allowing for local dimming, even in a large screen liquid crystal display, has been actively conducted.
However, in the case of an edge type backlight unit slimmer than the direct type backlight unit, it is advantageous in that an edge type backlight having a relatively small size, for example, 17 inches or less, may be manufactured to have a relatively reduced thickness. However, in the case of an LCD backlight light source having a larger size, that is, 40˜70 inches or more, obtaining sufficient brightness in the backlight light source may be difficult and brightness uniformity may consequently be deteriorated.
In addition, the edge type backlight unit may not be suitable to a partial driving method, such as local dimming, and the applying thereof may be difficult in a liquid crystal panel having a relatively large area.